In a conventional air conditioner known in the art, the compressor is controlled using an inverter so as to bring the indoor air temperature closer to an optimal temperature. Such an air conditioner controls the operation of the compressor based on the designated temperature, the indoor air temperature, the outlet air temperature, the suction pressure and the discharge pressure of the compressor, etc., as disclosed in Patent Document 1, for example. That is, an ordinary air conditioner detects, in addition to the indoor air temperature, at least one of the outlet air temperature, the suction pressure and the discharge pressure of the compressor, etc., and the operation of the compressor is controlled so as to bring these detected values closer to predetermined target values. Note that the designated temperature is typically set by operating a remote controller, and the designated temperature, the indoor air temperature, the outlet air temperature, and the suction pressure and the discharge pressure of the compressor are subjected to signal processing in the controller of the air conditioner, after which an inverter control signal is output from the controller to the compressor.
For air conditioners widely used in Japan, etc., it is a well known configuration where the compressor is controlled using an inverter as described above, but air conditioners widely used in North America, etc., typically have a unit called a “thermostat” (control interface), which is a remote controller with a function of the controller. The thermostat detects the indoor air temperature, and compares the detected indoor air temperature with the designated temperature so as to output an ON/OFF control signal to the compressor based on the comparison result.